Aligners with elastic layer

ABSTRACT

Improved orthodontic appliances, as well as related systems and methods, are provided. In one aspect, an orthodontic appliance can include a shell having a plurality of cavities shaped to receive a patient&#39;s teeth. The shell can include an exterior layer and an interior layer having a stiffness less than a stiffness of the exterior layer. A discontinuity can be formed in the exterior layer.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No.62/015,170, filed Jun. 20, 2014, which application is incorporatedherein by reference in its entirety.

BACKGROUND

Orthodontic procedures typically involve repositioning a patient's teethto a desired arrangement in order to correct malocclusions and/orimprove aesthetics. To achieve these objectives, orthodontic appliancessuch as braces, retainers, shell aligners, and the like can be appliedto the patient's teeth by an orthodontic practitioner. The appliance isconfigured to exert force on one or more teeth in order to effectdesired tooth movements. The application of force can be periodicallyadjusted by the practitioner (e.g., by altering the appliance or usingdifferent types of appliances) in order to incrementally reposition theteeth to a desired arrangement.

In some instances, however, current orthodontic appliances may not beable to effectively generate the forces needed to achieve the desiredtooth repositioning, or may not afford sufficient control over theforces applied to the teeth. The prior orthodontic approaches may oftenemploy a single appliance shell with homogeneous and/or continuousmaterial properties, which can provide less than ideal movement andcomfort. Additionally, the rigidity of some existing appliances mayinterfere with the ability of the appliance to be coupled to thepatient's teeth and may increase patient discomfort.

SUMMARY

Improved orthodontic appliances, as well as related systems and methods,are provided. An orthodontic appliance can include a shell having anexterior layer and an interior layer, with the exterior layer having agreater stiffness than the interior layer. A discontinuity can be formedin the exterior layer. When placed on a patient's teeth, the interactionof the interior layer with the discontinuity can exert forces on theunderlying teeth to elicit one or more desired tooth movements. Theappliances described herein may provide enhanced control over forcesexerted onto the teeth, thus enabling improved orthodontic treatmentprocedures.

Accordingly, in one aspect, an orthodontic appliance can include a shellhaving a plurality of cavities shaped to receive a patient's teeth. Theshell can include an exterior layer and an interior layer having astiffness less than that of the exterior layer. A discontinuity can beformed in the exterior layer.

Other objects and features of the present invention will become apparentby a review of the specification, claims, and appended figures.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1A illustrates a tooth repositioning appliance, in accordance withmany embodiments.

FIG. 1B illustrates a tooth repositioning system, in accordance withmany embodiments.

FIG. 2 illustrates a method of orthodontic treatment using a pluralityof appliances, in accordance with many embodiments.

FIG. 3A illustrates a portion of a layered orthodontic appliance, inaccordance with many embodiments.

FIGS. 3B through 3I illustrate discontinuities formed in an exteriorlayer of a layered orthodontic appliance, in accordance with manyembodiments.

FIG. 4A illustrates a layered orthodontic appliance having adiscontinuity, in accordance with many embodiments.

FIG. 4B illustrates the appliance of FIG. 4A when placed over apatient's teeth, in accordance with many embodiments.

FIG. 5A illustrates a layered orthodontic appliance having adiscontinuity, in accordance with many embodiments.

FIG. 5B illustrates the appliance of FIG. 5A when placed over apatient's teeth, in accordance with many embodiments.

FIG. 6 illustrates a method for fabricating an orthodontic appliance, inaccordance with many embodiments.

FIG. 7 illustrates a method for digitally planning an orthodontictreatment, in accordance with many embodiments.

FIG. 8 is a simplified block diagram of a data processing system, inaccordance with many embodiments.

DETAILED DESCRIPTION

A better understanding of the features and advantages of the presentdisclosure will be obtained by reference to the following detaileddescription that sets forth illustrative embodiments, in which theprinciples of embodiments of the present disclosure are utilized, andthe accompanying drawings.

Although the detailed description contains many specifics, these shouldnot be construed as limiting the scope of the disclosure but merely asillustrating different examples and aspects of the present disclosure.It should be appreciated that the scope of the disclosure includes otherembodiments not discussed in detail above. Various other modifications,changes and variations which will be apparent to those skilled in theart may be made in the arrangement, operation and details of themethods, systems, and apparatus of the present disclosure providedherein without departing from the spirit and scope of the invention asdescribed herein.

As used herein, A and/or B encompasses one or more of A or B, andcombinations thereof such as A and B.

The orthodontic appliances described herein, along with related systemsand methods, can be employed as part of an orthodontic treatmentprocedure in order to reposition one or more teeth, maintain a currentposition of one or more teeth, or suitable combinations thereof. Anorthodontic appliance can include an exterior layer and an interiorlayer. The exterior layer can be formed from a relatively rigid materialwhile the interior layer can be formed from a relatively elasticmaterial, such that the exterior layer is stiffer than the interiorlayer. One or more discontinuities can be formed in the exterior layerwhile leaving the interior layer intact. The geometry and configurationof the discontinuity can be selected such that when the appliance isworn by a patient, the discontinuity interacts with the elastic interiorlayer so as to generate forces suitable for repositioning one or more ofthe patient's teeth. In many embodiments, the interior layer resistsdeformation, deflection, and/or displacement of the discontinuity,thereby causing forces to be applied to one or more teeth. The materialproperties (e.g., stiffness) of the appliances described herein can bevaried via the discontinuities and/or elastic interior layer, thusaffording different force application to different teeth of thepatient's arch and, in some instances, more precise application ordelivery of one or more forces to teeth with decreased patientdiscomfort. Vary (varied) may mean that the variations (e.g.,differences in the values present in an appliance) in the correspondingmaterial properties are more than 10%, more than 25%, or more than 50%of the highest value of the corresponding material property present inthe appliance. Additionally, the techniques described herein can be usedto adjust the local compliance of the appliance, therefore improvingappliance fit and reducing patient discomfort.

Thus, in one aspect, an orthodontic appliance can include a shell havinga plurality of cavities shaped to receive a patient's teeth. The shellcan include an exterior layer and an interior layer having a stiffnessless than a stiffness of the exterior layer. A discontinuity can beformed in the exterior layer. In many embodiments, the exterior layerhas an elastic modulus within a range from about 10,000 psi to about700,000 psi and the interior layer has an elastic modulus within a rangefrom about 100 psi to about 8000 psi. In alternative embodiments, theinterior layer has an elastic modulus within a range from about 100 psito about 50,000 psi.

The design of the discontinuity can be varied as desired to elicit theappropriate tooth movements. For example, the discontinuity can includea cut formed in the exterior layer. The cut may extend at leastpartially around a protrusion formed in the exterior layer. In someinstances, the cut may be a closed cut, such as a cut enclosing a regionof the shell. The cut may extend from a buccal surface of the exteriorlayer to a lingual surface of the exterior layer. Alternatively or inaddition, the discontinuity can include a plurality of cuts in theexterior layer, such as a plurality of cuts that are parallel to eachother. The discontinuity can include a cut defining a flap in theexterior layer and a plurality of perforations near a joint portion ofthe flap.

The elements of the appliances described herein can be fabricated usingany suitable method. The exterior and interior layers may have beenthermoformed, for example. The discontinuity may have been etched orengraved in the exterior layer. In some instances, the discontinuity caninclude a shape etched in the exterior layer.

In another aspect, an orthodontic appliance can include a shell having aplurality of cavities shaped to receive a patient's teeth, the shellincluding a first layer and a second layer having a stiffness less thana stiffness of the first layer. A discontinuity can be formed in thefirst layer. In many embodiments, the first layer has an elastic moduluswithin a range from about 10,000 psi to about 700,000 psi and the secondlayer has an elastic modulus within a range from about 100 psi to about8000 psi. In alternative embodiments, the second layer has an elasticmodulus within a range from about 100 psi to about 50,000 psi. The firstlayer can comprise an exterior layer of the shell and the second layercan comprise an interior layer of the shell. Alternatively, the firstlayer can comprise an interior layer of the shell and the second layercan comprise an exterior layer of the shell.

The design of the discontinuity can be varied as desired. For example,the discontinuity can include a cut formed in the first layer. The cutmay extend at least partially around a protrusion formed in the firstlayer. In some instances, the cut may be a closed cut, such as a cutenclosing a region of the shell. The cut may extend from a buccalsurface of the first layer to a lingual surface of the first layer.Alternatively or in addition, the discontinuity can include a pluralityof cuts in the first layer, such as a plurality of cuts that areparallel to each other. The discontinuity can include a cut defining aflap in the first layer and a plurality of perforations near a jointportion of the flap.

The components of the appliances described herein can be produced in avariety of ways. The first and second layers may have been thermoformed,for example. The discontinuity may have been etched or engraved in thefirst layer. In some instances, the discontinuity can include a shapeetched in the first layer.

In another aspect, an appliance as described herein may be included in aseries of appliances so as to provide an orthodontic system forpositioning teeth. Such an orthodontic system can include a plurality oforthodontic appliances each comprising a shell including one or morecavities shaped to receive a patient's teeth. The appliances may besuccessively worn or wearable by the patient to move one or more teethfrom a first arrangement to a second arrangement. One or more of theappliances can include layered appliance as described herein. Forexample, a layered appliance of the system can include an applianceshell having a plurality of cavities shaped to receive the patient'steeth. The shell can include an exterior layer and an interior layerhaving a stiffness less than a stiffness of the exterior layer. Adiscontinuity can be formed in the exterior layer. In many embodiments,the exterior layer has an elastic modulus within a range from about10,000 psi to about 700,000 psi and the interior layer has an elasticmodulus within a range from about 100 psi to about 8000 psi. Inalternative embodiments, the interior layer has an elastic moduluswithin a range from about 100 psi to about 50,000 psi.

The geometry and configuration of the discontinuity can be selected soas to enable the application of one or more forces to a patient's teeth.The discontinuity can include a cut formed in the exterior layer. Forinstance, the cut may extend at least partially around a protrusionformed in the exterior layer. As another example, the cut may be aclosed cut, such as a cut enclosing a region of the shell. The cut mayextend from a buccal surface of the exterior layer to a lingual surfaceof the exterior layer. In some instances, the discontinuity can includea plurality of cuts in the exterior layer, such as a plurality of cutsthat are parallel to each other. The discontinuity can include a cutdefining a flap in the exterior layer and a plurality of perforationsnear a joint portion of the flap.

The exterior and interior layers of an appliance may have beenthermoformed so as to form an appliance shell. The discontinuity mayhave been etched or engraved in the exterior layer. For example, thediscontinuity can include a shape etched in the exterior layer.

In another aspect, an orthodontic system for repositioning a patient'steeth is provided. The orthodontic system can include a plurality oforthodontic appliances each comprising a shell including one or morecavities shaped to receive the patient's teeth. The appliances may besuccessively worn or wearable by the patient to move one or more teethfrom a first arrangement to a second arrangement. One or more of theappliances can include a layered appliance as described herein. Forexample, a layered appliance can include an appliance shell having aplurality of cavities shaped to receive the patient's teeth. Theappliance shell can include an first layer and an second layer having astiffness less than a stiffness of the first layer. A discontinuity canbe formed in the first layer. In many embodiments, the first layer hasan elastic modulus within a range from about 10,000 psi to about 700,000psi and the second layer has an elastic modulus within a range fromabout 100 psi to about 8000 psi. In alternative embodiments, the secondlayer has an elastic modulus within a range from about 100 psi to about50,000 psi. The first layer can comprise an exterior layer of theappliance shell and the second layer can comprise an interior layer ofthe appliance shell. Alternatively, the first layer can comprise aninterior layer of the appliance shell and the second layer can comprisean exterior layer of the appliance shell.

The geometry and configuration of the discontinuity can be selectedbased on forces desired to be applied to a patient's teeth. Thediscontinuity can include a cut formed in the first layer. For instance,the cut may extend at least partially around a protrusion formed in thefirst layer. As another example, the cut may be a closed cut, such as acut enclosing a region of the shell. The cut may extend from a buccalsurface of the first layer to a lingual surface of the first layer. Insome instances, the discontinuity can include a plurality of cuts in thefirst layer, such as a plurality of cuts that are parallel to eachother. The discontinuity can include a cut defining a flap in the firstlayer and a plurality of perforations near a joint portion of the flap.

The first and second layers of an appliance may have been thermoformedso as to form an appliance shell. The discontinuity may have been etchedor engraved in the first layer. For example, the discontinuity caninclude a shape etched in the first layer.

In another aspect, a method for creating an orthodontic appliance asdescribed herein can include providing a shell having a plurality ofcavities shaped to receive a patient's teeth. The shell can include anexterior layer and an interior layer having a stiffness less than astiffness of the exterior layer. In many embodiments, the exterior layerhas an elastic modulus within a range from about 10,000 psi to about700,000 psi and the interior layer has an elastic modulus within a rangefrom about 100 psi to about 8000 psi. In alternative embodiments, theinterior layer has an elastic modulus within a range from about 100 psito about 50,000 psi. The exterior and interior layers of the shell mayhave been thermoformed. A discontinuity can be formed in the exteriorlayer. The process of forming the discontinuity may include creating acut in the exterior layer, such as a cut extending at least partiallyaround a protrusion formed in the exterior layer. The cut may be aclosed cut. In some instances, the cut may extend from a buccal surfaceof the exterior layer to a lingual surface of the exterior layer. Thediscontinuity may also be formed by creating a plurality of cuts in theexterior layer, and the plurality of cuts may be parallel to each other.The discontinuity can include a cut defining a flap in the exteriorlayer and a plurality of perforations near a joint portion of the flap.As another example, forming the discontinuity may include etching orengraving the discontinuity in the exterior layer. The etching of thediscontinuity in the exterior layer may include etching a shape in theexterior layer.

In another aspect, a method for creating an orthodontic appliance asdescribed herein is provided. The method can include providing a shellhaving a plurality of cavities shaped to receive a patient's teeth. Theshell can include a first layer and a second layer having a stiffnessless than a stiffness of the first layer. In many embodiments, the firstlayer has an elastic modulus within a range from about 10,000 psi toabout 700,000 psi and the second layer has an elastic modulus within arange from about 100 psi to about 8000 psi. In alternative embodiments,the second layer has an elastic modulus within a range from about 100psi to about 50,000 psi. The first layer can comprise an exterior layerof the shell and the second layer can comprise an interior layer of theshell. Alternatively, the first layer can comprise an interior layer ofthe shell and the second layer can comprise an exterior layer of theshell.

The first and second layers of the shell may have been thermoformed. Adiscontinuity can be formed in the first layer. The process of formingthe discontinuity may include creating a cut in the first layer, such asa cut extending at least partially around a protrusion formed in thefirst layer. The cut may be a closed cut. In some instances, the cut mayextend from a buccal surface of the first layer to a lingual surface ofthe first layer. The discontinuity may also be formed by creating aplurality of cuts in the first layer, and the plurality of cuts may beparallel to each other. The discontinuity can include a cut defining aflap in the first layer and a plurality of perforations near a jointportion of the flap. As another example, forming the discontinuity mayinclude etching or engraving the discontinuity in the first layer. Theetching of the discontinuity in the first layer may include etching ashape in the first layer.

Turning now to the drawings, in which like numbers designate likeelements in the various figures, FIG. 1A illustrates an exemplary toothrepositioning appliance or aligner 100 that can be worn by a patient inorder to achieve an incremental repositioning of individual teeth 102 inthe jaw. The appliance can include a shell (e.g., a continuous polymericshell or a segmented shell) having teeth-receiving cavities that receiveand resiliently reposition the teeth. An appliance or portion(s) thereofmay be indirectly fabricated using a physical model of teeth. Forexample, an appliance (e.g., polymeric appliance) can be formed using aphysical model of teeth and a sheet of suitable layers of polymericmaterial. In some instances, a physical appliance is directlyfabricated, e.g., using rapid prototyping fabrication techniques, from adigital model of an appliance. An appliance can fit over all teethpresent in an upper or lower jaw, or less than all of the teeth. Theappliance can be designed specifically to accommodate the teeth of thepatient (e.g., the topography of the tooth-receiving cavities matchesthe topography of the patient's teeth), and may be fabricated based onpositive or negative models of the patient's teeth generated byimpression, scanning, and the like. Alternatively, the appliance can bea generic appliance configured to receive the teeth, but not necessarilyshaped to match the topography of the patient's teeth. In some cases,only certain teeth received by an appliance will be repositioned by theappliance while other teeth can provide a base or anchor region forholding the appliance in place as it applies force against the tooth orteeth targeted for repositioning. In some cases, many or most, and evenall, of the teeth will be repositioned at some point during treatment.Teeth that are moved can also serve as a base or anchor for holding theappliance as it is worn by the patient. Typically, no wires or othermeans will be provided for holding an appliance in place over the teeth.In some cases, however, it may be desirable or necessary to provideindividual attachments or other anchoring elements 104 on teeth 102 withcorresponding receptacles or apertures 106 in the appliance 100 so thatthe appliance can apply a selected force on the tooth. Exemplaryappliances, including those utilized in the Invisalign® System, aredescribed in numerous patents and patent applications assigned to AlignTechnology, Inc. including, for example, in U.S. Pat. Nos. 6,450,807,and 5,975,893, as well as on the company's website, which is accessibleon the World Wide Web (see, e.g., the url “invisalign.com”). Examples oftooth-mounted attachments suitable for use with orthodontic appliancesare also described in patents and patent applications assigned to AlignTechnology, Inc., including, for example, U.S. Pat. Nos. 6,309,215 and6,830,450.

FIG. 1B illustrates a tooth repositioning system 110 including aplurality of appliances 112, 114, 116. Any of the appliances describedherein can be designed and/or provided as part of a set of a pluralityof appliances used in a tooth repositioning system. Each appliance maybe configured so a tooth-receiving cavity has a geometry correspondingto an intermediate or final tooth arrangement intended for theappliance. The patient's teeth can be progressively repositioned from aninitial tooth arrangement to a target tooth arrangement by placing aseries of incremental position adjustment appliances over the patient'steeth. For example, the tooth repositioning system 110 can include afirst appliance 112 corresponding to an initial tooth arrangement, oneor more intermediate appliances 114 corresponding to one or moreintermediate arrangements, and a final appliance 116 corresponding to atarget arrangement. A target tooth arrangement can be a planned finaltooth arrangement selected for the patient's teeth at the end of allplanned orthodontic treatment. Alternatively, a target arrangement canbe one of many intermediate arrangements for the patient's teeth duringthe course of orthodontic treatment, which may include various differenttreatment scenarios, including, but not limited to, instances wheresurgery is recommended, where interproximal reduction (IPR) isappropriate, where a progress check is scheduled, where anchor placementis best, where palatal expansion is desirable, where restorativedentistry is involved (e.g., inlays, onlays, crowns, bridges, implants,veneers, and the like), etc. As such, it is understood that a targettooth arrangement can be any planned resulting arrangement for thepatient's teeth that follows one or more incremental repositioningstages. Likewise, an initial tooth arrangement can be any initialarrangement for the patient's teeth that is followed by one or moreincremental repositioning stages.

FIG. 2 illustrates a method 200 of orthodontic treatment using aplurality of appliances, in accordance with many embodiments. The method200 can be practiced using any of the appliances or appliance setsdescribed herein. In step 210, a first orthodontic appliance is appliedto a patient's teeth in order to reposition the teeth from a first tootharrangement to a second tooth arrangement. In step 220, a secondorthodontic appliance is applied to the patient's teeth in order toreposition the teeth from the second tooth arrangement to a third tootharrangement. The method 200 can be repeated as necessary using anysuitable number and combination of sequential appliances in order toincrementally reposition the patient's teeth from an initial arrangementto a target arrangement. The appliances can be generated all at the samestage or in sets or batches (e.g., at the beginning of a stage of thetreatment), or one at a time, and the patient can wear each applianceuntil the pressure of each appliance on the teeth can no longer be feltor until the maximum amount of expressed tooth movement for that givenstage has been achieved. A plurality of different appliances (e.g., aset) can be designed and even fabricated prior to the patient wearingany appliance of the plurality. After wearing an appliance for anappropriate period of time, the patient can replace the currentappliance with the next appliance in the series until no more appliancesremain. The appliances are generally not affixed to the teeth and thepatient may place and replace the appliances at any time during theprocedure (e.g., patient-removable appliances). The final appliance orseveral appliances in the series may have a geometry or geometriesselected to overcorrect the tooth arrangement. For instance, one or moreappliances may have a geometry that would (if fully achieved) moveindividual teeth beyond the tooth arrangement that has been selected asthe “final.” Such over-correction may be desirable in order to offsetpotential relapse after the repositioning method has been terminated(e.g., permit movement of individual teeth back toward theirpre-corrected positions). Over-correction may also be beneficial tospeed the rate of correction (e.g., an appliance with a geometry that ispositioned beyond a desired intermediate or final position may shift theindividual teeth toward the position at a greater rate). In such cases,the use of an appliance can be terminated before the teeth reach thepositions defined by the appliance. Furthermore, over-correction may bedeliberately applied in order to compensate for any inaccuracies orlimitations of the appliance.

Although the above steps show a method 200 of orthodontic treatmentusing a plurality of appliances in accordance with embodiments, a personof ordinary skill in the art will recognize many variations based on theteaching described herein. Some of the steps may comprise sub-steps.Many of the steps may be repeated as often as beneficial to thetreatment. One or more steps of the method 200 may be applied to anysuitable orthodontic appliance, such as the embodiments describedherein.

Various embodiments and configurations of appliances can be consideredfor the orthodontic systems and treatments described herein. Forexample, an appliance can include a plurality of layers, including atleast one relatively elastic layer and at least one relatively rigidlayer. Herein, “relatively elastic” and “relatively rigid” may indicatethat the relatively rigid layer is more rigid (stiff) than therelatively elastic layer. For example, the (relatively) rigid layer mayhave an elastic modulus within a range from about 10,000 psi to about700,000 psi, and the (relatively) elastic layer may have an elasticmodulus within a range from about 100 psi to about 8000 psi, or fromabout 100 psi to about 50,000 psi. The elastic and rigid layers can bearranged in any suitable manner to form an appliance, such as with theelastic layer on the interior of the appliance and the rigid layer onthe exterior of the appliance. “Interior” may be used herein to refer toportions of an appliance that are adjacent to or approximately adjacentto the received teeth when the appliance is worn, while “exterior” maybe used to refer to portions of an appliance opposite from orapproximately opposite from the received teeth when the appliance isworn. “Interior” and “exterior” may also be used herein to denoterelative positioning rather than absolute positioning. In alternativeembodiments, other configurations can be used, e.g., the appliance canbe formed with the elastic layer on the exterior and the rigid layer onthe interior.

The number of layers within a layered orthodontic appliance can bevaried as desired. The appliance can include only a single elastic layerand only a single rigid layer. Alternatively, the appliance can includeother layers in addition to the elastic layer and rigid layer, e.g.,intermediate layers interspersed between the elastic and rigid layers.Optionally, the appliance can include a plurality of elastic layers anda plurality of rigid layers. As will be appreciated, the layeredappliances described herein can impart forces on one or more of thepatient's teeth so as to elicit various tooth movements in accordancewith a desired treatment procedure.

FIG. 3A illustrates a portion of a layered orthodontic appliance 300, inaccordance with many embodiments. The appliance 300 can include a shell302 having one or more teeth-receiving cavities 303 shaped toaccommodate a patient's teeth. The shell 302 can include an exteriorlayer 304 and interior layer 306. Accordingly, when the appliance 300 isworn over a patient's teeth, the interior layer 306 may contact theteeth, while the exterior layer 304 may not be in contact with theteeth. In some instances, the inner surface of the interior layer 306may be covered by one or more additional layers of material (not shown),such that the interior layer 306 does not directly contact the teeth.These additional layers may be provided primarily as an interface forimproving the contact between the shell 302 and the teeth and/orgingiva, and thus may be relatively thin compared to the exterior andinterior layers 304, 306. Optionally, one or more additional layers canalso be situated at other locations of the shell 302, e.g., between theexterior layer 304 and interior layer 306, over the outer surface of theexterior layer 304, etc.

The exterior and interior layers 304, 306 may each span the entirety ofthe appliance 300, or only certain portions of the appliance 300. Inmany embodiments, the exterior and interior layers 304, 306 extend fromthe lingual surface 308 to the buccal surface 310 of the appliance 300,thereby covering the lingual, occlusal, and buccal surfaces of the teethreceived within the appliance 300. Optionally, one or more portions ofthe exterior layer 304 and/or interior layer 306 may also extend overthe gingiva. The exterior and interior layers 304, 306 may overlap eachother such that they cover the same or similar portions of the patient'steeth when the appliance 300 is worn. The exterior layer 304 andinterior layer 306 can be coupled to each other (e.g., by one or morediscrete attachment points and/or over one or more continuous attachmentareas) at the overlapping portions, thereby forming a bilayered shellstructure. In many embodiments, the exterior and interior layers 304,306 overlap over the entirety of the appliance 300 so that the wholeappliance 300 is at least bilayered. Alternatively, the exterior andinterior layers 304, 306 may not overlap over some portions of theappliance 300, such that the teeth received within these portions arecovered by the exterior layer 304 without the interior layer 306, orvice-versa. Some portions of the appliance 300 may be formed from othermaterials or components, and thus may not include either of the exterioror interior layers 304, 306.

The exterior layer 304 may be relatively rigid and the interior layer306 may be relatively elastic. Consequently, the stiffness of theinterior layer 306 may be less than the stiffness of the exterior layer304. The properties (e.g., stiffness) of the appliance 300 at thebilayered portions may be determined primarily by the properties of theexterior layer 304, with relatively little contribution from the elasticinterior layer 306. Accordingly, these portions of the appliance 300 maybe relatively rigid and may experience little or no deformation whenplaced on the patient's teeth. Conversely, portions of the appliance 300where there are discontinuities in the exterior layer 304 may permitgreater contributions from the interior layer 306 and therefore may berelatively flexible and/or deformable, as discussed in further detailbelow.

The properties of the exterior and interior layer 304, 306 can be variedas desired. For example, the interior layer 306 may have an elasticmodulus of about 600 psi, or within a range from about 100 psi to about8000 psi, or from about 100 psi to about 50,000 psi. The exterior layer304 may have an elastic modulus of approximately 100,000 psi, or withina range from approximately 10,000 psi to approximately 700,000 psi. Theelastic modulus of the interior layer 306 may be approximately 100%,90%, 80%, 70%, 60%, 50%, 40%, 30%, 30%, or 10% of the elastic modulus ofthe exterior layer 304. In many embodiments, the stiffness of each layeris related to the thickness of the layer. The exterior and interiorlayers 304, 306 may have the same thickness or different thicknesses.For instance, the thickness of the interior layer 304 may beapproximately 0.02 mm, or within a range from approximately 0.01 mm toapproximately 1.0 mm. The thickness of the exterior layer 306 may beapproximately 0.05 mm, or within a range from approximately 0.02 mm toapproximately 1.0 mm. The thickness of the interior layer 304 may beapproximately 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 30%, or 10% ofthe thickness of the exterior layer 306.

In alternative embodiments, the exterior layer 304 may be relativelyelastic and the interior layer 306 may be relatively rigid, such thatthe stiffness of the exterior layer 304 is less than the stiffness ofthe interior layer 306. It shall be understood that although variousembodiments presented herein illustrate a shell with a rigid exteriorlayer and elastic interior layer, the concepts of the present disclosureare also applicable to alternative configurations of layered appliances,e.g., appliances including a shell with an elastic exterior layer andrigid interior layer.

A layered appliance as described herein can include one or morediscontinuities formed in one or more of the layers, e.g., the exteriorlayer, the interior layer, the elastic layer, the rigid layer, orcombinations thereof. In many embodiments, the one or morediscontinuities are formed in only a single layer, e.g., the exteriorlayer only, the interior layer only, the elastic layer only, or therigid layer only, such that the other layer(s) do not include anydiscontinuities. Although various embodiments herein describediscontinuities formed in only a rigid exterior layer of a layeredorthodontic appliance, it shall be understood that alternativeembodiments can include discontinuities formed in other layers, e.g., anelastic interior layer, a rigid interior layer, etc.

A discontinuity can include any suitable number and combination of cuts,flaps, apertures (e.g., openings, windows, gaps, notches), ordeformations (e.g., protrusions, indentations, reliefs) formed in anysuitable portion of the layer, such as an exterior layer, (e.g., in abuccal, lingual, occlusal, and/or gingival surface). The dimensions(e.g., length, width, depth, surface area, etc.) and/or the shape of thediscontinuity can be calculated, for instance, to achieve a specifieddegree of appliance compliance. A discontinuity may be linear, curved,curvilinear, circular, elliptical, triangular, square, rectangular,polygonal, or any other regular or irregular shape, or suitable portionsor combinations thereof. A discontinuity can be oriented along anydirection, such as along an occlusal-gingival direction, a mesial-distaldirection, or a buccal-lingual direction.

The number, geometry, and configuration of the discontinuities can beselected so as to modulate the local properties (e.g., compliance orstiffness) of the appliance and/or influence the forces imparted ontothe patient's teeth via the appliance. The forces may be provided whollyor in part by the interaction of the layer (e.g., an elastic interiorlayer) with the discontinuity, and may result from deformations,deflections, and/or displacements of the discontinuity and/or interiorlayer when the appliance is worn on a patient's teeth. The geometry andconfiguration of the discontinuities described herein can be selected tocontrol the magnitude and/or direction of the forces applied to theteeth.

FIG. 3B illustrates a discontinuity 312 formed in the exterior layer 304of the appliance 300, in accordance with many embodiments. Thediscontinuity 312 can be formed solely in the exterior layer 304 suchthat the interior layer 306 is left intact. The interior layer 306 maybe exposed through the discontinuity 312. The presence of thediscontinuity 312 may alter the properties of the appliance 300 at ornear the discontinuity 312. For example, in many embodiments, theexposed interior layer 306 is less rigid than the exterior layer 304,such that the local compliance of the appliance 300 at or near thediscontinuity 312 may be increased compared to other portions of theappliance 300. In some instances, the discontinuity 312 may bedeformable (e.g., changeable with respect to shape, size) and/ordisplaceable, e.g., when the appliance is worn, which may also producean increase in the local compliance of the appliance. The amount oflocal compliance can be used to control the resulting forces (e.g.,magnitude, direction) exerted on the underlying teeth. Furthermore, theinterior layer 306 may interact with the discontinuity 312, such as byexerting forces on the discontinuity 312 or on portions of the exteriorlayer 304 near the discontinuity 312. These forces may result wholly orin part from deformation or displacement of the discontinuity 312 and/orinterior layer 306 when the appliance 300 is worn, as described ingreater detail below. The forces generated by the interaction of theinterior layer 306 and the discontinuity 312 may be transmitted to theunderlying teeth via the shell 302, thereby causing the repositioning ofone or more teeth. The forces can be applied directly to the teeth bythe shell 302. Alternatively, the shell 302 can apply force indirectly,e.g., via one or more attachments mounted on one or more teeth (notshown). In such instances, the discontinuity 312 can be shaped toaccommodate the attachment.

In FIG. 3B, the discontinuity 312 is depicted as an arcuate cut forminga semicircular flap 314 in the exterior layer 304. Alternatively, othergeometries for the cut and flap 314 can be used (e.g., elliptical,square, rectangular, triangular, polygonal, etc.). The edges of the flap314 may be joined to the edges of adjacent portions of the exteriorlayer 304 by the underlying interior layer 306. The flap 314 may beoutwardly and/or inwardly deflectable relative to the surroundingportions of the exterior layer 304. In some instances, the arcuate cutcan extend around a feature formed in the shell 302, such as aprotrusion, indentation, or relief. Optionally, the arcuate cut can besituated adjacent to or near a tooth-mounted attachment when theappliance 300 is worn by a patient.

FIGS. 3C through 3F illustrate other exemplary discontinuities that maybe provided as part of the appliance 300, in accordance with manyembodiments. FIG. 3C illustrates a discontinuity formed as a closed cut316. The closed cut 316 encloses a region 318 of the exterior layer 304,thus separating it from the rest of the exterior layer 304. The interiorlayer 306 may span the closed cut 316 so as to join the edges of theenclosed region 318 to the edges of the adjacent portions of theexterior layer 304. The closed cut 316 may be a circular cut, asdepicted herein, or any other suitable shape. The separated region 318defined by the closed cut 316 may include a feature such as aprotrusion, indentation, or relief. The separated region 318 may bedisplaceable relative to the surrounding portions of the exterior layer304.

FIG. 3D illustrates a discontinuity formed as an elongate linear cut320. The linear cut 320 may extend from the buccal surface to thelingual surface of the exterior layer 304. The dimensions of the linearcut 320 can be varied as desired. For example, the linear cut 320 mayextend from the buccal edge to the lingual edge of the appliance 300,thus separating the exterior layer 304 into discrete segments 322, 324.The segments 322, 324 may be joined to each other by the portions of theinterior layer 306 spanning the linear cut 320. The segments 322, 324may be displaced relative to each other when the appliance 300 is placedon the patient's teeth. In many embodiments, the linear cut 320 ispositioned adjacent to or near an interproximal region between teeth,with the segments 322, 324 at least partially covering the teethadjacent to the interproximal region. Accordingly, the segments 322, 324can be shaped to receive teeth or portions thereof.

FIG. 3E illustrates a discontinuity formed as a plurality of elongatelinear cuts 326. Any suitable number of linear cuts 326 can be used. Thelinear cuts 326 may have the same or similar dimensions (e.g., length,width). Similar may mean that the variation of the dimension may be nomore than 50%, no more than 25%, or no more than 10% of the maximumvalue of a corresponding dimension in the appliance. Alternatively, someof the cuts 326 may have different dimensions than other cuts 326, forexample, variations of more than 10%, more than 25%, or more than 50% ofthe maximum value of a corresponding dimension in the appliance. Some orall of the linear cuts 326 may be parallel cuts. Conversely, some or allof the linear cuts 326 may not be parallel to each other. The linearcuts 326 can be spaced apart from each other by a specified distance.The spacing between the linear cuts 326 may be uniform or may vary. Theportions of the exterior layer 304 adjacent the linear cuts 326 may bejoined by the interior layer 306 underlying the cuts 326. The cuts 326may deform (e.g., stretch, widen) when the appliance 300 is worn by thepatient.

FIG. 3F illustrates a discontinuity formed as an etched shape 328 in theexterior layer 304. The shape 328 can be etched only partially into theexterior surface of the exterior layer 304, such that the interior layer306 is not exposed. Alternatively, the etching may penetrate through theentire depth of the exterior layer 304 so as to expose the interiorlayer 306. The etching of the exterior layer 304 may reduce thethickness of the exterior layer 304 at the discontinuity, which mayalter the properties (e.g., stiffness) of the appliance 300 at or nearthe discontinuity. For instance, the presence of the etched shape 328may increase the influence of the interior layer 306 on the localcompliance of the appliance 300 (e.g., reduce the local compliance).

The etched shape 328 is depicted herein as a collapsible structureincluding a ring 330 and a disk 332, although other geometries can alsobe used. The interior layer 306 may join the ring 330 and disk 332. Inthe collapsed configuration of the etched shape 328 (e.g., when theappliance 300 is not being worn by a patient), the ring 330 and disk 332may lie in approximately the same plane as the surrounding portions ofthe exterior layer 304. In the expanded configuration of the etchedshape 328 (e.g., when the appliance 300 is worn by the patient), thering 330, disk 332, and intervening portions of the interior layer 306can protrude outwards from the surrounding exterior layer 304 so as toform a receptacle. The receptacle can be shaped, for instance, toreceive an attachment mounted on the underlying tooth, and to exertforce onto the tooth via the attachment.

FIGS. 3G through 3I each illustrate a discontinuity formed as a cut 334defining a flap 336 in the exterior layer 304, similar to the embodimentdepicted in FIG. 3B. The flap 336 can be deflected relative to thesurrounding portions of the exterior layer 304, e.g., to accommodate anunderlying tooth surface, shell feature, and/or tooth attachment. Inorder to increase the movement range of the flap 336 and/or reduce themagnitude of the forces needed to deflect the flap 336, it may bebeneficial to modify the exterior layer 304 to reduce the flexingresistance of the material at or near the joint portion of the flap 336.This may be accomplished by forming one or more discontinuities in theexterior layer 304 at or near the joint portion. In many embodiments,the discontinuities can be positioned so as to define the joint portionthat flexes during deflection of the flap 336. Any suitable number andcombination of discontinuities can be used, and the geometry (e.g.,size, shape) and configuration of the discontinuities can be varied asdesired in order to provide the appropriate amount of flexing resistanceat or near the joint portion. For instance, FIG. 3G illustrates aplurality of perforations 338 formed in the exterior layer 304 at thejoint portion of the flap 336. The perforations 338 may be oval-shaped,as depicted in FIG. 3G, or any other suitable geometry (e.g., circular,square, triangular, polygonal, etc.). As another example, FIG. 3Hillustrates a plurality of small circular perforations 340 formed in theexterior layer 304 at the joint portion. At least some of thediscontinuities presented herein may extend through the entire thicknessof the exterior layer 304, thereby exposing the underlying interiorlayer 306. In alternative embodiments, the discontinuities may onlyextend partially through the exterior layer 304, thereby reducing thethickness of the material at or near the joint portion. For example,FIG. 3I illustrates a groove 342 formed in the exterior layer 304 nearthe joint portion of the flap 336. The ends of the groove 342 maycontact the cut 334. In alternative embodiments, the ends of the groove342 may not be in contact with the cut 334. The groove 342 can be etchedor engraved into the exterior layer 304 to a depth that is less than thethickness of the exterior layer 304. The dimensions (e.g., length,width, depth) and shape (e.g., linear, curved, curvilinear) of thegroove 342 can be configured to optimize the flexibility of the flap336.

The layered appliances described herein can be worn by a patient so asto apply force onto one or more underlying teeth, and thereby effectvarious movements of the teeth. The direction and extent of theresultant tooth movements can be determined based on the geometry,configuration, and properties of the discontinuity, interior layer,and/or exterior layer. Furthermore, the appliances described herein mayincorporate various features (e.g., protrusions, indentations, grooves,notches, buttons, reliefs) formed in the appliance shell (e.g., in theinterior and/or exterior layer) that can engage the teeth at discretepoints and/or over continuous regions so as to further influence themagnitude and/or direction of the forces imparted on the teeth. Thenumber, geometry, and configuration of such features can be selectedbased on the desired movements for the targeted teeth.

FIGS. 4A and 4B illustrate a layered orthodontic appliance 400 having adiscontinuity 402, in accordance with many embodiments. The appliance400 can include a shell 404 formed from an exterior layer 406 andelastic interior layer 408, with a portion of the interior layer 408exposed through the discontinuity 402 (depicted herein as an elongatelinear cut). In other embodiments, no portion of the interior layer maybe exposed through the discontinuity, e.g., in embodiments where thediscontinuity does not penetrate through the entire exterior layer. Whenthe appliance 400 is placed on a patient's teeth 410 (depicted in FIG.4B), the discontinuity 402 may be deformed by the intentional mismatchbetween the patient's current tooth arrangement and the tootharrangement specified by the geometry of the appliance 400. Forinstance, the elongate linear cut of the discontinuity 402 may bewidened into an elongate aperture. Additionally, one or more portions ofthe interior layer 408 spanning the discontinuity 402 may also bedeformed (e.g., stretched) according to the deformation of thediscontinuity 402. The resistance of the interior layer 408 todeformation may cause forces to be exerted on the discontinuity 402and/or the surrounding portions of the exterior layer 406. Some or allof these forces may be transmitted to the underlying teeth, therebyeliciting movements of one or more teeth with respect to up to sixdegrees of freedom of motion (e.g., translation, rotation, intrusion,extrusion, tipping, torqueing, etc.). For example, the interaction ofthe discontinuity 402 and interior layer 408 may produce tooth movementsthat reduce an interproximal space between teeth (e.g., arrows 412).Alternatively or additionally, the appliance 400 may be used to produceother types of tooth movements, such as tooth movements increasing aninterproximal space between teeth (e.g., to correct malocclusions, toaccommodate an implant or other dental prosthesis, etc.). As the teethare repositioned, the deformation of the discontinuity 402 and/or theinterior layer 408 may decrease, thus diminishing the amount of forceexpressed on the teeth by the appliance 400.

FIGS. 5A and 5B illustrate cross-sectional views of a layeredorthodontic appliance 500 having a discontinuity 502, in accordance withmany embodiments. The appliance 500 can include a shell 504 having anexterior layer 506 and elastic interior layer 508. The discontinuity 502can be a cut forming a flap in the exterior layer 506, similar to theembodiments depicted in FIGS. 3B and 3G through 3I. The edges of the cutmay be joined by the interior layer 508. The shell 504 can include afeature such as a protrusion 510 (e.g., a button, knob, etc.) situatedon the flap and extending into the interior cavity of the appliance 500.When a tooth 512 is received within the appliance 500, the protrusion510 and flap may be displaced outwards by the surface topography of thetooth 512. The elastic interior layer 508 may resist the displacement byexerting force on the exterior layer 506 at or near the discontinuity502, thereby pulling the protrusion 510 and flap inwards against thetooth surface (e.g., arrow 514). The exerted force may be transmitted tothe tooth 512 primarily at the point of contact between the surface ofthe tooth 512 and the protrusion 510. The application of force to thecontact point can elicit various movements of the tooth 512, such as atipping movement. In some instances, a plurality of protrusions can beused in combination with a plurality of discontinuities so as to providea plurality of contact points for more precise application of forces tothe tooth.

Various different embodiments or configurations may be considered forthe layered appliances described herein. For example, an appliance mayaccommodate various different configurations for elastic and/or rigidlayers, including different compositions and/or structures of elasticand/or rigid materials. Material forming a layer may include a singlecontinuous layer of material or multiple layers of the same material,different materials, or a combination of some layers of the samematerial and one or more layers of different material(s). Properties ofthe material layer such as resiliency, elasticity, hardness/softness,color, and the like can be determined, at least partially, based on theselected material, layers of material, and/or layer thickness. In someinstances, the layer can be configured such that one or more propertiesare uniform along a length or portion of the layer (or entire layer).Additionally, one or more properties of the layer may vary along alength or portion of the layer (or entire layer). Vary (or variable) mayfor example mean that the variations of the one or more properties ishigher than 10%, higher than 25%, or higher than 50% of the highestvalue of the corresponding property/properties of the elastic material.For example, a layer may have substantially uniform thickness along alength or portion, or may vary along a length/portion. Substantiallyuniform may mean that the variations (e.g., the absolute value of thedifference between any two values of one property with regard to theappliance) of the one or more properties is no higher than 50%, nohigher than 25%, or no higher than 10% of the highest value of thecorresponding property/properties of the elastic material. As will beappreciated, characteristics of the layer or layer may be selected so asto affect the force application to the patient's teeth or tooth movementaspects of a particular treatment desired.

FIG. 6 illustrates a method 600 for fabricating an orthodonticappliance, in accordance with many embodiments. The method 600 can beapplied to any embodiment of the orthodontic appliances describedherein.

In step 610, a shell having a plurality of cavities shaped to receiveteeth is provided. The shell can include a first layer and a secondlayer having a stiffness less than a stiffness of the first layer, suchthat the first layer is relatively rigid and the second layer isrelatively elastic. For example, the first layer can be an exteriorlayer of the shell and the second layer can be an interior layer of theshell. Alternatively, the first layer can be an interior layer of theshell and the second layer can be an exterior layer of the shell. Thesecond and first layers can be formed from any suitable material orcombination of materials. For example, the first layer and/or secondlayer can be formed from biocompatible materials suitable fororthodontic use, such as latex. In some instances, the first and secondlayers are transparent, translucent, or colored, so as to improve theaesthetics of the appliance when worn by a patient. The first layer(e.g., the relatively rigid layer) can be fabricated from materialssimilar or corresponding to those used for conventional single layeredappliance shells, such as polymeric sheets. The materials for the firstlayer may be more rigid than those typically used for single layeredshells. The second layer (e.g., the relatively elastic layer) can befabricated from any suitable elastic material, and such materials may beprovided as strips, bands, sheets, meshes, coatings, layers, or suitablecombinations thereof. The characteristics of the elastic material (e.g.,length, width, thickness, area, shape, cross-section, stiffness, etc.)may be homogeneous throughout the bulk of the elastic material, or maybe variable. For example, different portions of the second layer mayhave different thicknesses, thereby altering the local compliance of theappliance shell. Furthermore, in some instances, the second layer mayhave anisotropic characteristics. As an example, the second layer may berelatively compliant along a first direction, and less compliant (ornoncompliant) along a second direction. The directionality of the secondlayer can be used to control the direction of the resultant forcesapplied to the teeth. Optionally, the second layer can be formed withtopological features (e.g., embossing, brushing, texturing, roughening,etc.) to enhance surface friction between the shell and the enamel ofthe received teeth. Such features can be used, for instance, to improvethe ability of the shell to grip onto teeth when worn by the patient.

The shell can be fabricated using any suitable method, such asthermoforming, rapid prototyping, stereolithography, or computernumerical control (CNC) milling. For example, the first and secondlayers may be thermoformed to form the shell. The layers may bethermoformed simultaneously or sequentially. An interior layer may bethermoformed first and an exterior layer subsequently thermoformed ontop of the interior layer. The thermoforming process may directly bondthe first and second layers together (e.g., via thermal bonding) withoutthe use of adhesives or other indirect bonding methods. Alternatively orin addition, adhesive agents can be used to couple the first and secondlayers to each other. In some instances, an exterior layer may be formedfirst, with an interior layer being subsequently coupled to the exteriorlayer (e.g., by dipping, spraying, extruding, coating, etc.), orvice-versa. The bilayered shells described herein can be fabricatedbased on a physical or digital model of the patient's teeth. The modelcan be generated from dental impressions or scanning (e.g., of thepatient's intraoral cavity, of a positive or negative model of thepatient's intraoral cavity, or of a dental impression formed from thepatient's intraoral cavity).

In step 620, a discontinuity is formed in the first layer. Any methodsuitable for creating cuts in the first layer or removing material fromthe first layer can be used to create one or more discontinuities. Forexample, the discontinuity can be engraved or etched in the first layer(e.g., using CNC-based or laser-based methods). The discontinuity may beformed without disturbing the second layer. The discontinuity maypenetrate through the entire thickness of the first layer so as toexpose the underlying second layer, or may penetrate only partiallythrough the first layer so that the second layer is not exposed. In manyembodiments, the discontinuity is located only in the first layer, suchthat the second layer is left intact.

Although the above steps show a method 600 for fabricating anorthodontic appliance in accordance with embodiments, a person ofordinary skill in the art will recognize many variations based on theteaching described herein. Some of the steps may comprise sub-steps.Many of the steps may be repeated as often as beneficial to thetreatment. One or more steps of the method 600 may be applied to anysuitable orthodontic appliance, such as the embodiments describedherein. The order of the steps can be varied. For example, inalternative embodiments, a layered orthodontic appliance can befabricated by first providing a first (e.g., exterior) layer, andforming a discontinuity in the first layer as described above. The firstlayer can subsequently be coupled to an elastic second (e.g., interior)layer to form a bilayered shell, using any of the techniques discussedherein.

Appliance fabrication or design can make use of one or more physical ordigital representations of the patient's teeth. Representations of thepatient's teeth can include representations of the patient's teeth in acurrent arrangement, and may further include representations of thepatient's teeth repositioned in one or more treatment stages. Treatmentstages can include a desired or target arrangement of the patient'steeth, such as a desired final arrangement of teeth. Treatment stagescan also include one or more intermediate arrangements of teeth (e.g.,planned intermediate arrangements) representing arrangements of thepatient's teeth as the teeth progress from a first arrangement (e.g.,initial arrangement) toward a second or desired arrangement (e.g.,desired final arrangement).

FIG. 7 illustrates a method 700 for digitally planning an orthodontictreatment and/or design or fabrication of an appliance, in accordancewith many embodiments. The method 700 can be applied to any of thetreatment procedures described herein and can be performed by anysuitable data processing system.

In step 710, a digital representation of a patient's teeth is received.The digital representation can include surface topography data for thepatient's intraoral cavity (including teeth, gingival tissues, etc.).The surface topography data can be generated by directly scanning theintraoral cavity, a physical model (positive or negative) of theintraoral cavity, or an impression of the intraoral cavity, using asuitable scanning device (e.g., a handheld scanner, desktop scanner,etc.).

In step 720, one or more treatment stages are generated based on thedigital representation of the teeth. The treatment stages can beincremental repositioning stages of an orthodontic treatment proceduredesigned to move one or more of the patient's teeth from an initialtooth arrangement to a target arrangement. For example, the treatmentstages can be generated by determining the initial tooth arrangementindicated by the digital representation, determining a target tootharrangement, and determining movement paths of one or more teeth in theinitial arrangement necessary to achieve the target tooth arrangement.The movement path can be optimized based on minimizing the totaldistance moved, preventing collisions between teeth, avoiding toothmovements that are more difficult to achieve, or any other suitablecriteria.

In step 730, at least one orthodontic appliance is fabricated based onthe generated treatment stages. For example, a set of appliances can befabricated to be sequentially worn by the patient to incrementallyreposition the teeth from the initial arrangement to the targetarrangement. Some of the appliances can be shaped to accommodate a tootharrangement specified by one of the treatment stages. Alternatively orin combination, some of the appliances can be shaped to accommodate atooth arrangement that is different from the target arrangement for thecorresponding treatment stage. For example, as previously describedherein, an appliance may have a geometry corresponding to anovercorrected tooth arrangement. Such an appliance may be used to ensurethat a suitable amount of force is expressed on the teeth as theyapproach or attain their desired target positions for the treatmentstage. As another example, an appliance can be designed in order toapply a specified force system on the teeth and may not have a geometrycorresponding to any current or planned arrangement of the patient'steeth.

The appliance set may include one or more of the layered appliancesdescribed herein. The properties of the interior and exterior layers ofthese appliances (e.g., geometry, configuration, materialcharacteristics) and the configuration of one or more discontinuities inthe exterior layer can be selected to elicit the tooth movementsspecified by the corresponding treatment stage. In many embodiments, alayered appliance associated with a treatment stage may omit one or moreportions of the interior layer or exterior layer. The determination ofwhich portions to omit may be based on the particular tooth movements tobe achieved during the treatment stage. For example, when contacting atooth, the relatively elastic interior layer may produce increasedfrictional forces compared to the exterior layer. Accordingly, theremoval of portions of the interior layer may in some instancesfacilitate the movement of the tooth relative to the appliance.Conversely, the presence of the interior layer at certain locations maybe beneficial in embodiments where increased friction between the toothsurface and the appliance enhances force application onto the tooth.

The design of the layered appliances provided herein can be determinedvia suitable computer software or other digital-based approaches. Forexample, computer modeling strategies can be used to determine suitableforce systems including one or more forces and/or torques to be appliedto the teeth to elicit the desired tooth movements. The arrangement andproperties of the interior and exterior layers and the configuration ofone or more discontinuities in the exterior layer can be designed toprovide the specified forces and/or torques when the appliance is wornby the patient during an appropriate stage of treatment. Additionalexamples of digital modeling and force analysis techniques suitable foruse with the embodiments provided herein are described in applicationSer. Nos. 12/623,340, 12/324,714, and 13/365,167, and in U.S. Pat. No.8,439,672, the disclosures of which are herein incorporated by referencein their entirety. The digital models created using such methods may beused as input to a computer-controlled fabrication system forfabricating appliances.

Although the above steps show method 700 of digitally planning anorthodontic treatment and/or design or fabrication of an appliance inaccordance with embodiments, a person of ordinary skill in the art willrecognize many variations based on the teaching described herein. Someof the steps may comprise sub-steps. Many of the steps may be repeatedas often as beneficial to the treatment. One or more steps of the method700 may be applied to the fabrication of any orthodontic appliance, suchas the embodiments described herein. Some of the steps may be optional,and the order of the steps can be varied. In some instances, staging ofvarious arrangements or treatment stages may not be necessary for designand/or fabrication of an appliance. As illustrated by the dashed line inFIG. 7, design and/or fabrication of an orthodontic appliance, andperhaps a particular orthodontic treatment, may include use of arepresentation of the patient's teeth (e.g., receive a digitalrepresentation of the patient's teeth 710), followed by design and/orfabrication of an orthodontic appliance based on a representation of thepatient's teeth in the arrangement represented by the receivedrepresentation. For example, a positive or negative model may begenerated based on the representation of the patient's teeth (e.g., asin step 710), followed by thermoforming of the interior and exteriorlayers onto the positive or negative model to form an appliance shell asdescribed in various embodiments herein.

FIG. 8 is a simplified block diagram of a data processing system 800that may be used in executing methods and processes described herein, inaccordance with many embodiments. The data processing system 800typically includes at least one processor 802 that communicates with oneor more peripheral devices via bus subsystem 804. These peripheraldevices typically include a storage subsystem 806 (memory subsystem 808and file storage subsystem 814), a set of user interface input andoutput devices 818, and an interface to outside networks 816. Thisinterface is shown schematically as “Network Interface” block 816, andis coupled to corresponding interface devices in other data processingsystems via communication network interface 824. Data processing system800 can include, for example, one or more computers, such as a personalcomputer, workstation, mainframe, laptop, and the like.

The user interface input devices 818 are not limited to any particulardevice, and can typically include, for example, a keyboard, pointingdevice, mouse, scanner, interactive displays, touchpad, joysticks, etc.Similarly, various user interface output devices can be employed in asystem of the invention, and can include, for example, one or more of aprinter, display (e.g., visual, non-visual) system/subsystem,controller, projection device, audio output, and the like.

Storage subsystem 806 maintains the basic required programming,including computer readable media having instructions (e.g., operatinginstructions, etc.), and data constructs. The program modules discussedherein are typically stored in storage subsystem 806. Storage subsystem806 typically includes memory subsystem 808 and file storage subsystem814. Memory subsystem 808 typically includes a number of memories (e.g.,RAM 810, ROM 812, etc.) including computer readable memory for storageof fixed instructions, instructions and data during program execution,basic input/output system, etc. File storage subsystem 814 providespersistent (non-volatile) storage for program and data files, and caninclude one or more removable or fixed drives or media, hard disk,floppy disk, CD-ROM, DVD, optical drives, and the like. One or more ofthe storage systems, drives, etc may be located at a remote location,such coupled via a server on a network or via the internet/World WideWeb. In this context, the term “bus subsystem” is used generically so asto include any mechanism for letting the various components andsubsystems communicate with each other as intended and can include avariety of suitable components/systems that would be known or recognizedas suitable for use therein. It will be recognized that variouscomponents of the system can be, but need not necessarily be at the samephysical location, but could be connected via various local-area orwide-area network media, transmission systems, etc.

Scanner 820 includes any means for obtaining a digital representation(e.g., images, surface topography data, etc.) of a patient's teeth(e.g., by scanning physical models of the teeth such as casts 821, byscanning impressions taken of the teeth, or by directly scanning theintraoral cavity), which can be obtained either from the patient or fromtreating professional, such as an orthodontist, and includes means ofproviding the digital representation to data processing system 800 forfurther processing. Scanner 820 may be located at a location remote withrespect to other components of the system and can communicate image dataand/or information to data processing system 800, for example, via anetwork interface 824. Fabrication system 822 fabricates appliances 823based on a treatment plan, including data set information received fromdata processing system 800. Fabrication machine 822 can, for example, belocated at a remote location and receive data set information from dataprocessing system 800 via network interface 824.

As used herein A and/or B encompasses one or more of A or B, andcombinations thereof such as A and B.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. Numerous differentcombinations of embodiments described herein are possible, and suchcombinations are considered part of the present disclosure. In addition,all features discussed in connection with any one embodiment herein canbe readily adapted for use in other embodiments herein. It is intendedthat the following claims define the scope of the invention and thatmethods and structures within the scope of these claims and theirequivalents be covered thereby.

What is claimed is:
 1. An orthodontic appliance, comprising: a shellhaving a plurality of cavities shaped to receive a patient's teeth,wherein the shell comprises a first layer and a second layer having astiffness less than a stiffness of the first layer; and a discontinuityformed in the first layer.
 2. The appliance of claim 1, wherein thefirst layer comprises an exterior layer of the shell and the secondlayer comprises an interior layer of the shell.
 3. The appliance ofclaim 1, wherein the first layer comprises an interior layer of theshell and the second layer comprises an exterior layer of the shell. 4.The appliance of claim 1, wherein the discontinuity comprises a cut inthe first layer.
 5. The appliance of claim 4, wherein the cut extends atleast partially around a protrusion formed in the first layer.
 6. Theappliance of claim 4, wherein the cut comprises a closed cut.
 7. Theappliance of claim 4, wherein the cut extends from a buccal surface ofthe first layer to a lingual surface of the first layer.
 8. Theappliance of claim 1, wherein the discontinuity comprises a plurality ofcuts in the first layer.
 9. The appliance of claim 8, wherein theplurality of cuts are parallel to each other.
 10. The appliance of claim1, wherein the first and second layers have been thermoformed.
 11. Theappliance of claim 1, wherein the discontinuity has been etched orengraved in the first layer.
 12. The appliance of claim 11, wherein thediscontinuity comprises a shape etched in the first layer.
 13. Theappliance of claim 1, wherein the discontinuity comprises a cut defininga flap in the first layer and a plurality of perforations near a jointportion of the flap.
 14. The appliance of claim 1, wherein the firstlayer has an elastic modulus within a range from about 10,000 psi toabout 700,000 psi and the second layer has an elastic modulus within arange from about 100 psi to about 50,000 psi.
 15. An orthodontic system,comprising: a plurality of orthodontic appliances each comprising ashell including one or more cavities shaped to receive a patient'steeth, wherein the appliances are successively wearable by the patientto move one or more teeth from a first arrangement to a secondarrangement, and wherein at least one of the appliances comprises: anappliance shell having a plurality of cavities shaped to receive thepatient's teeth, wherein the appliance shell comprises a first layer anda second layer having a stiffness less than a stiffness of the firstlayer, and a discontinuity formed in the first layer.
 16. The system ofclaim 15, wherein the first layer comprises an exterior layer of theappliance shell and the second layer comprises an interior layer of theappliance shell.
 17. The system of claim 15, wherein the first layercomprises an interior layer of the appliance shell and the second layercomprises an exterior layer of the appliance shell.
 18. The system ofclaim 15, wherein the discontinuity comprises a cut in the first layer.19. The system of claim 18, wherein the cut extends at least partiallyaround a protrusion formed in the first layer.
 20. The system of claim18, wherein the cut comprises a closed cut.
 21. The system of claim 18,wherein the cut extends from a buccal surface of the first layer to alingual surface of the first layer.
 22. The system of claim 15, whereinthe discontinuity comprises a plurality of cuts in the first layer. 23.The system of claim 22, wherein the plurality of cuts are parallel toeach other.
 24. The system of claim 15, wherein the first and secondlayers have been thermoformed.
 25. The system of claim 15, wherein thediscontinuity has been etched or engraved in the first layer.
 26. Thesystem of claim 25, wherein the discontinuity comprises a shape etchedin the first layer.
 27. The system of claim 15, wherein thediscontinuity comprises a cut defining a flap in the first layer and aplurality of perforations near a joint portion of the flap.
 28. Thesystem of claim 15, wherein the first layer has an elastic moduluswithin a range from about 10,000 psi to about 700,000 psi and the secondlayer has an elastic modulus within a range from about 100 psi to about50,000 psi.
 29. A method for creating a orthodontic appliance, themethod comprising: providing a shell having a plurality of cavitiesshaped to receive a patient's teeth, wherein the shell comprises a firstlayer and a second layer having a stiffness less than a stiffness of thefirst layer; and forming a discontinuity in the first layer.
 30. Themethod of claim 29, wherein the first layer comprises an exterior layerof the shell and the second layer comprises an interior layer of theshell.
 31. The method of claim 29, wherein the first layer comprises aninterior layer of the shell and the second layer comprises an exteriorlayer of the shell
 32. The method of claim 29, wherein forming thediscontinuity comprises creating a cut in the first layer.
 33. Themethod of claim 32, wherein the cut extends at least partially around aprotrusion formed in the first layer.
 34. The method of claim 32,wherein the cut comprises a closed cut.
 35. The method of claim 32,wherein the cut extends from a buccal surface of the first layer to alingual surface of the first layer.
 36. The method of claim 29, whereinforming the discontinuity comprises creating a plurality of cuts in thefirst layer.
 37. The method of claim 36, wherein the plurality of cutsare parallel to each other.
 38. The method of claim 29, wherein thefirst and second layers have been thermoformed.
 39. The method of claim29, wherein forming the discontinuity in the first layer comprisesetching or engraving the discontinuity in the first layer.
 40. Themethod of claim 39, wherein etching the discontinuity in the first layercomprises etching a shape in the first layer.
 41. The method of claim29, wherein forming the discontinuity comprises forming a cut defining aflap in the first layer and a plurality of perforations near a jointportion of the flap.
 42. The method of claim 29, wherein the first layerhas an elastic modulus within a range from about 10,000 psi to about700,000 psi and the second layer has an elastic modulus within a rangefrom about 100 psi to about 50,000 psi.